Trim mowers, also sometimes referred to as utility mowers, may be used to mow the smaller and/or enclosed rough and fringe areas on golf courses. These areas may require a trim mower having a relatively narrow cut width because the areas may include undulating terrain, or may be too small or confined for larger mowing machines. Trim mowers may include three cutting units powered by and attached to a traction vehicle. For example, two front cutting units may be positioned forward of the vehicle's front pair of wheels, and a rear cutting unit may be between the front wheels and a single rear wheel used for steering. The rear cutting unit may cut a swath between the two front cutting units that overlaps the swaths cut by the two front cutting units.
Trim mowers have a tendency to “crab” when operated on side slopes that have relatively steep inclines or undulations that are common on many golf courses. Crabbing refers to the rear wheel tracking or sliding downhill from the centerline of the trim mower. Crabbing may cause the trim mower to leave uncut strips of grass. This occurs when the rear cutting unit tracks or slides downhill so much that it no longer can overlap the two front cutting units.
To prevent or minimize uncut strips, trim mowers may be designed with additional overlap between the front and rear cutting units. However, greater overlap also can reduce a trim mower's cutting width, resulting in lower productivity of the trim mower in flatter areas. A trim mower is needed having high versatility, and that will prevent or minimize uncut strips without sacrificing productivity.
When trim mowers are used to cut grass at or near the edge of a golf course hazard such as a sand trap or bunker, or other golf course feature, the machine's weight may cause the bunker wall to collapse, especially in sandy soil conditions. Additionally, a trim mower weighing 1000 pounds or more may slide into a sand trap or bunker, get stuck, become high centered, or experience reduced stability. A trim mower is needed that will reduce the risk of damage to golf course features such as sand traps or bunkers. A trim mower is needed that will maintain stability and minimize the risk of sliding into a sand trap or bunker, becoming high centered or stuck.
Efforts have been made to design and make trim mowers that solve one or more of these problems. For example, U.S. Pat. Nos. 6,032,441 and 6,351,929 relate to a triplex trim mower with a pair of laterally adjustable cutting units. The cutting units are supported by a lateral carrier frame which is slidably engaged to a lateral support frame. A hydraulic cylinder permits the carrier frame to be laterally displaced with respect to the vehicle frame to reach the edge of a bunker or sand trap while the machine maintains a distance from that feature. When trimming around an obstacle on a slope with the cutting units shifted to the downhill side, the trim mower may experience reduced stability because all cutting units are shifted by a single carrier which supports its own weight along with weight of the cylinders and lift arms. When this weight and the cutting units are shifted to the downhill side, the center of gravity of the machine is moved into a less favorable position that can lead to reduced stability. If both cutting units are shifted to one side of the machine with the single carrier frame, the opposite side tire may roll on uncut turf, resulting in poor cut quality and an unsightly cut pattern.
A shift mechanism for a trim mower cutting units is needed that minimizes the reduction of stability when one or more cutting units are shifted and extended outwardly, especially while the machine is on steep slopes. A shift mechanism is needed that will minimize the shift in the vehicle's center of gravity if one or more cutting units are extended outwardly. A shift mechanism is needed that will not cause the uphill tire to roll on uncut turf, and that will help a trim mower achieve a better cut quality and cut pattern.
Shift mechanisms have been proposed to move cutting units laterally outwardly. For example, U.S. Pat. No. 2,882,978 relates to a selectably slidable, laterally offset mower for trimming beneath overhanging obstacles such as low tree branches. U.S. Pat. No. 4,873,818 relates to a similar mower that provides increased offset capability. U.S. Pat. Nos. 4,893,456 and 5,483,789 relate to single cutting decks that can be laterally displaced from a conventional centered position to a laterally extended position. These devices are not well suited and have not been adapted for use on trim mowers that are used to cut rough and fringe areas on a golf course.
A shift mechanism for a trim mower is needed that allows a cutting unit to reach and mow grass in small or enclosed areas of golf courses, especially around the edges of hazards such as sand traps and bunkers, but that will not sacrifice productivity when mowing other areas. A shift mechanism for a trim mower is needed that is capable of increasing the mower's cutting width, or increasing the overlap between front and rear cutting units. A shift mechanism for a trim mower is needed that helps the vehicle maintain stability when mowing on side hills, or if a cutting unit is moved laterally. A shift mechanism is needed that can reduce the risk of damage to the edges of sand traps and bunkers.